The invention relates to a method of manufacturing foamed panels, specifically panels having a rigid substructure and a foam layer. In the preferred embodiment of the invention, the foam is covered by a finishing layer. Foamed panels are useful in many applications, including lining the interior of automobiles. A rigid panel, generally made of a plastic or a woodstock base material, is provided with a covering. The covering may be a vinyl sheet or other formable material. To provide an attractive feel and appearance, foam material is placed between the rigid substructure and the covering. Various components having a hollow or partially hollow cross-section are often placed adjacent the substructure. Automotive instrument panels, for example, have reinforcement beams or ducts placed adjacent the panel. It is desirable to integrally mold the substructure with these beams or ducts. However, using conventional manufacturing techniques, the substructure cannot be completely supported by the mold die and the pressure from the foaming operation deforms the unsupported sections of the panel.
A method for producing a close-mold foamed composite panel is shown and described in U.S. Pat. No. 4,303,728, issued to Houdek et al, Dec. 1, 1981. Houdek et al teaches a method of producing a foamed composite panel which does not have hollow or partially hollow sections by placing a finishing layer in the cavity of a first die. A rigid substructure is overlaid the finishing layer and spaced apart therefrom. An second die is overlaid the rigid substructure. The first and second dies are brought together and a space is maintained between the sheet and rigid substructure. A foaming material is injected within the space and allowed to cure. The second die generally completely supports the rigid substructure and prevents deflection of the substructure during the foaming. Expansion of the foam is limited to the space defined between the rigid substructure and sheet. The second die prevents deflection of the rigid substructure by the expanding foam. Deflection of the rigid substructure would cause an increase in the space and thickness of the foam. Houdek et al teaches a second die having an interior surface conforming generally to a rigid substructure. The rigid substructure is nearly completely supported by the second die during the foaming process.
It is desirable in some applications, such as automotive instrument panels, to produce a rigid substructure having hollow or partially hollow sections for the ventilating ducts, support brackets, reinforcement ribbing, and the like. These hollow and partially hollow sections prevent completely supporting the rigid substructure by the die during the foaming process. When the rigid substructure is not completely supported by the die, deflection of the rigid substructure by the expanding foam occurs and produces a finished article having an irregular surface finish.
In some instances, it may be desirable to produce articles having a channel section with a nonuniform foam thickness. These channels will have thicker sections of foam in the area of the channel. Panels produced by conventional methods often experience greater foam shrinkage in the channel area than the thinner areas of the panel. This greater foam shrinkage produces ripples in the finished article.
U.S. Pat. No. 4,791,019, issued Dec. 13, 1988, to Ohta et al, teaches a foamed interior panel which does not include a rigid substructure. Glass fibers are added to the foam material to create a semirigid polyurethane foam layer. The urethane foam eliminates the need for a rigid panel. Ohta et al does not teach molding an instrument panel having integral ducts which are used to support the foamed layer.
U.S. Pat. No. 4,806,293, issued to Akiyama et al, on Feb. 21, 1989, teaches a method of producing a molded article from a foamed thermoplastic material by injecting a thermoplastic resin in a mold cavity. The resin begins to foam and causes the expansion of the article in the mold cavity. The dies are operable to control compression pressure of the foamed article during the mold process. Akiyama et al does not teach foaming a space adjacent a rigid substructure and maintaining the pressure in the space to avoid deflection of the rigid substructure. The foamed article in Akiyama et al is not integrally molded onto a sheet member or a rigid substructure.
It is an object of the present invention to provide a method of manufacturing a foamed article having a rigid substructure which is not completely supported by a die.
It is a further object of the present invention to provide a method of making a molded article on a rigid substructure which is not supported by a die.
It is a further object of the present invention to produce a foamed instrument panel having integrally molded ducts. It is another object of the present invention to provide a panel having a nonuniform thickness of foam which displays a smooth exterior surface appearance.
It is a further object of the present invention to produce a foamed instrument panel having integrally molded ducts.